Gas turbine for driving airscrews



March 15; 1949.

M. H. SEDI LLE GAS TURBINE FOR DRIVING AIRSCREWS Filed Feb. 27, 1946 IAN/euro)? Patented Mar. 15, 1949 UNITED STATES PATENT OFFICE.

2,464,724 Y GAS TURBINE FOR DRIVING AIRSCREWS Marcel Henri Louis Sdille, Paris, France, assignor to Societe Rateau (Societe Anonyme), Paris, France, a company of France, and Ren Anxionnaz, Paris, France Application February 27,1946, Serial No. 650,565 In France April 4, 1945 2 Claims. 1 This invention relates to gas turbines for driving airscrews.

It is known that the propulsion of very fast vehicles and in particular, aeroplanes, may be wardly in a direction opposite to that of the movement of the vehicle, by means of a reaction tube or nozzle, it is possible to obtain by reaction a supplementary propelling power which adds to the power developed by the airscrew.

It is an advantage to increase thereaction power as much as possible for the following two reasons:

1. This power provides a direct propelling effect without passing through the intermediary of the turbine and th airscrew, it permits therefore of a reduction in dimensions of the airscrew of the turbine and, in consequence, ,in the weight of the said machines.

2. The efiect produced by the reaction nozzle may be increased by providing supplementary burners to reheat the exhaust gases from the turbine before their expansion in the reaction nozzle.

Extra power is obtained in this way at the cost of some reduction in the efliciency of the propelling plant, but this extra power can be more substantial as the fraction of the total power normally used in the reaction jet is the greater. This extra power can be of unlimited duration, while, as known, ordinary engines driving airscrews without reaction can furnish extra power only during short time intervals.

The part of the power which passes into the reaction jet cannot, however, be increased very substantially without reducing the emciency of the propelling plant.

The device forming the object of the invention permits of increasing, without the above mentioned disadvantage, that part of the power used in the reaction jet, and, in consequence, of profiting by the advantages above enumerated. According to the invention there is provided a bypass for air connecting the air compressor--and, preferably, an intermediate stage of this compressorto a chamber which precedes th reaction nozzle and in which adjustable heating means are arranged for heating the mixture of exhaust gases and pure air before its admission to the reaction nozzle.

The following description relating to the accompanying drawing, given only by way of example, explains how the invention may be carried into effect.

Fig. 1 illustrates in axial section a known form of construction of a gas turbine driving an airscrew in the propulsion of an aeroplane, and Fig.

'2 illustrates in axial section a propulsion device according to' the invention. I

An aeroplane propelling unit such as illustrated by way of example in Fig. 1 will first be considcred. It comprises an airscrew a driven by a gas turbine plant comprising an axial compressor b, one or more combustion chambers cprovided with burners d, and a gas turbine e. The power delivered by the gas turbine is equal to the sum of the powers absorbed by the airscrew a and the compressor b. Assuming suflicient efliciency of.

the turbine and of the compressor and .a suitable selection of the power absorbed by the-screw, the pressure of the gases, at the outlet of the turbine,

will be greater than that of the ambient atmosphere. They might therefore expand in a nozzle ,2 extending in a direction opposite to that of the movement of the vehicle, where they acquire in this way a velocity V1, providing a propelling power which is added to that of the airscrew. As above stated this velocity may be increased in order to furnish extra power by increasing the temperature of the gases by a burner g.

If the speed of the aeroplane is-denoted by Von, the power per unit of weight of the fluid evolved which is used in the reaction nozzle is:

9 being the gravity acceleration.

In the same conditions the propelling thrust (per unit of weight) due to the reaction of the ases is:

and the corresponding. useful powerof propulsion due to the reaction:

The useful efiiciency of the reaction device will therefore be It appears from this formula that the efficiency is reduced when the thermal drop and consequently the velocity V1 in the reaction nozzle are increased. The output of fluid which is evolved being, according to the arrangement adopted, the same in the gas turbine and in the reaction nozzle, if for the same total power brought into action, the power of the gas turbine is reduced and the power utilised in the reaction'nozzle is increased in proportion, the velocity V1 is increased. The eiiiciency p decreases and might even become less than the product of the efiiciency of the airscrew by the efiiciency of the gas turbine, which product is the emciency for normal use of the power contained in the gases without reaction. it then, it is desired to increase too much the part of the power used in reaction, the total efilciency will be reduced, which therefore provides a limit in this direction.

Owing to the invention it is possible to make the reaction power independent of the exhaust velocity of the gases at their issuing from the turblne by giving different values to the quantities of fluid which are evolved in the turbine, on the one hand, and in the reaction nozzle, on the other band.

Fig. 2 illustrates diagrammatically by way of example an embodiment of the invention. The air compressor is subdivided into two parts b1 b2 with an intermediate air bleed h. A fraction of the flow of compressed air through in is passed through the tube i to the reaction nozzle 1', the remaining part of the air being subjected to a supplementary compression at be, then to heating in the combustion chambers provided with burners d, and finally to expansion in the gas turbine e. The yield from the reaction nozzle is thus inc'.eased and the temperature of the gases before reaching it is reduced by admixture with cold air. This results in increasing the efficiency for use in propulsion of the jet of exhaust gas in the nozzle by decreasing the velocity V1 without reducing the power used in direct reaction re a consequence of the increase of the delivery w ht of fluid which is evolved.

The propulsion efficiency being excellent, it is then possible, without any inconvenience, to increase in substantial proportions the part of the power used in reaction relatively to the part used for driving the airscrew. Since moreover the temperature upstream of the nozzle is reduced by an addition of cold air, a more substantial extra power at equal maximum temperature above the reacton nozzle may be produced by burning fuel in the burner or burners g, in therchamber f1 which precedes the said nozzle.

As will be understood, it is possible to regulate the by-passed air passing to the reaction nozzle and the ratio of expansion in this latter by suitabledevices such for example as a movable annular throttle 1 acting on the outlet section or the air upstream of the reaction nomle, or by any other equivalent device.

What I claim is:

1. In a vehicle, particularly an aeroplane, having for its propulsion means an airscrew and a reaction jet nozzle, a combination for controlling the quantitative relationship 01. the powers dissipated in the airscrew and in the reaction Jet nozzle, respectively, said combination comprising: a gas turbine for driving said airscrew, multistage air compressing means, the high pressure stage at least of which is operated by the said gas turbine, a combustion chamber fed by said high pressure stage and delivering motive hot gases to said turbine, a second chamber receiving the exhaust gases of said turbine and opening into said reaction jet nozzle, 9. by-pass connecting an intermediate stage of said air compressing means with the said second chamber, adjustable heating means in said second chamber for heating the mixture of exhaust gases and pure air before its admission in the said jet nozzle, and means for controlling the output of pure air flowing through said by-pass.

'2. The combination as claimed in claim 1, wherein the last named means comprises an annular throttle disposed at the junction of said bypass and said second chamber.

MARCEL HENRI LOUIS smnirn.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Flight, Br. magazine, Sept. 25, 1941, pp. -192. 

